This application is related to copending application Ser. No. 43,606, entitled "A Welding Apparatus With Time Interval Control, " filed in the U.S. Patent Office on May 29, 1979.
The present invention relates to an apparatus for short-arc welding of the kind which includes a controllable current source, means for controllably feeding a wire-like consumable electrode comprising additive material to the weld location, and a control unit for automatically adjusting the current source in dependence upon the welding sequence, said current source being arranged to provide welding periods divided into short-circuit intervals, arc intervals and optionally also rest intervals.
In short-arc welding operations, the additive material is fed to the welding zone in the form of a continuously advanced wire through which the welding current also flows. One characteristic of short-arc welding is that the wire electrode is brought into direct contact with the weld location at closely following points of time, so-called short-circuit intervals, and short circuits the welding current circuit until the outermost end of the wire has melted. Each short-circuit interval is followed by a so-called arc interval, during which an arc burns between the outermost end of the wire and the weld location. The arc interval can be interrupted, either spontaneously as a result of the arc being extinguished due to the wire again short circuiting the said current circuit, or because the power is too low to maintain the arc, or the arc may be extinguished positively by automatically interrupting the supply of current by means of a control unit for the current source prior to the entry of the short-circuiting state. In the two latter cases there is obtained a so-called rest interval, during which current to the weld location is broken. The short-arc welding sequence is thus pulse-like or periodic, each welding period comprising a short-circuit interval and an arc interval, and optionally also a rest interval.
In short-arc welding it is essential that the penetration can be controlled and monitored, if a good weld is to be obtained. To this end, means have been proposed by which either the power or the current can be automatically regulated to a pre-selected constant value chosen with respect to the desired penetration. One serious disadvantage with such means, is that they do not take into account the supply of additive material and the supply of energy during short-circuit intervals of the weld periods, and hence the result is dependent upon the expertise of the welder with respect to the selection of welding parameters, the feed of the additive material, and the manual handling of the welding tool during a welding operation.